Astroparticle Physics
Astroparticle physics is a new multidisciplinary field of research that deals with the study of particles coming from the Universe.

It is the field of research where particle physics, astronomy, astrophysics and cosmology converge: Particle physics deals with the study of the intimate structure of matter and the fundamental laws that govern their interactions, e.g. the physics of the smallest scale of the Universe. Astronomy and astrophysics, study the structure of the Universe (largest scale) and its evolution from the initial hot Big Bang (smallest scale). It is cosmology that links the theory of particle physics with that of the very early Universe. Any discovery in particle physics has an immediate consequence on the understanding of the Universe and, inversely, discoveries in cosmology have fundamental impact on theories of the infinitely small.

Until the early 1950s, cosmic rays - charged high-energy particles from outer space –were our main source of information for advances in knowledge about the nature of matter in the Universe. Then, particle accelerators opened the path to tremendous progress, providing high-energy particle beams to investigate the structure of matter. Today, however, we are going back to study cosmic rays because new kinds of detectors allow us to detect cosmic rays with energies far beyond the limits of accelerators.

As the field of Astroparticle physics develops, it is opening up new observing windows in astronomy. For the first time, light or more generally electromagnetic waves are not the only messengers from distant objects in the Universe, as we begin to observe very high-energy cosmic rays, neutrinos, or gravitational waves.

By comparing observations through different windows and at various energies, we aim to learn more about high-energy cosmic phenomena in the Universe and the violent processes that give rise to them. A series of astrophysical objects demand an interdisciplinary, multi-wavelength and multi-messenger approach for their comprehension. Furthermore, astrophysical sites of violent phenomena can be used as a laboratory to test the structure of the fundamental laws of particle physics and gravitation.

On the instrumentation and methodology side, particle physics detector techniques are used to detect astrophysical objects and conversely astrophysics methods are used to study topics of importance to particle physics (e.g. dark matter and energy).

Up to now, many pioneering experiments in Astroparticle Physics have been on a scale whereby they could be implemented by small teams funded nationally. This has now changed such that, except for some specific topics the most promising new projects need large multidisciplinary teams on a European scale or even world level. The rapid development of the field has led to the design and the construction of infrastructures whose size, complexity and cost reach often levels requiring the cooperation of several scientific teams from different countries. These infrastructures are of three kinds:

  • Underground laboratories (shielding the experiments from the cosmic muon background), where room and services are provided to receive experimental devices.
  • “Observatories” or “telescopes” or “antennas” on earth whose optimal size is generally large due to the weakness (for gravitational waves) or the scarcity (for very high energy gamma rays, neutrinos or very high energy cosmic rays) of the signals which are to be detected.
  • Satellite observatories of high energy gamma rays, cosmic rays or gravitational waves.

Europe is already a leading player in the field of Astroparticle Physics and European teams have already made significant contributions in many key areas. There are about 2000 European scientists involved in the field in some fifty laboratories. The consolidated cost of the current European program is close to 400 million Euros. The investment cost of current experiments range from ten to a hundred million euros per experiment. Future projects will increase the scale of investment by at least a factor 5. The consolidation of the existing coordination of the different projects at the European level has become a necessity.

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